1. Field of the Invention
The present invention relates to an optical module that provides a body with a stem where a semiconductor optical device is mounted thereon and extends a plurality of lead pins therefrom, and a cap resistance-welded to the stem to form a cavity where the semiconductor optical device is air-tightly sealed.
2. Related Prior Art
An optical module generally provides the body, which includes the stem that is made of metal, mounts the semiconductor optical device and holds the lead pins air-tightly sealed by the seal glass, and the metal cap with a glass plate or a lens in a top thereof to pass the optical signal therethrough. The cap is typically resistance-welded to the metal stem.
In the resistance-welding, at least one of the cap and the stem forms a rib or interposes a member with a projection between the cap and the stem, and a quite large current is supplied and concentrated on the tip portion of the projection to melt the projection as pressing the cap and the stem to each other to fix both members.
A Japanese Patent Application published as JP-H06-140644A has disclosed an optical module that provides a lens holder covering the cap and providing a V-groove into which members for the resistance-welding are set. This arrangement can narrower the are coming in contact at the welding, which enables to increase the current density for the welding, that is, the total current may be reduced and the excess heating of the devices installed in the optical module may be escaped. However, the arrangement of the lens holder mentioned above covers the side of the stem where the projection is also provided. Although it reliably secures the air-tightness, the arrangement inevitably widens the module.
The resistance-welding is necessary to press the members to be welded to each other, which causes the deformation of the welded portions because the mechanical stress is applied to a portion where the Joule heat is generated at the welding. For the optical module, as shown in the prior document mentioned above, the cap is resistance-welded to the stem. The portion adjacent and periphery to the projection of the cap or the stem may be stuck out compared to those before the welding.
Another Japanese Patent Application published as JP-2003-320462A has suggested an arrangement that enables to escape the module from the above subject, in which the projection accompanies with hollows in both sides of the projection. The melted and deformed portion of the projection may be set within the hollows. However, this arrangement of the projection may be unfavorable from the viewpoint of the airtightness after the resistance-welding.
The present invention is to provide an arrangement for the resistance-welding that enables, even when the welding accompanies the mechanical deformation and the large Joule heat, to absorb the deformation and to escape the device in the module from the heating.